Field of the Invention
The present invention relates to an image display apparatus and a method for controlling the image display apparatus.
Description of the Related Art
Liquid-crystal display apparatuses include a liquid-crystal panel, a backlight arranged on a rear side of the liquid-crystal panel, and a control circuit that controls operations of the liquid-crystal panel and the backlight. In recent years, for reproduction of a wide color gamut, power saving, and the like, liquid-crystal display apparatuses have become widespread which have a white LED (a LED (light-emitting diode) that emits white light), three-primary-color LEDs, or the like as backlight light-emitting elements. The three-primary-color LEDs include a red LED, a green LED, and a blue LED.
Continuously viewing light with a short wavelength in a visible wavelength region (for example, blue light) for a long time is considered to lead to health hazards to the eyes. The health hazards caused by blue light include eye strain, a headache, a change in a biological rhythm. For example, the blue light has a wavelength which is not less than 380 nm and not more than 495 nm. In the JIS standards, such a function as illustrated in FIG. 1 is defined as a hazard function that represents a corresponding relation between the wavelength of light and the degree of the adverse effect of light on human bodies. The hazard function illustrated in FIG. 1 is referred to as a “blue-light hazard function” because the hazard function indicates a high degree (the degree of the adverse effect) for the wavelength of blue light. Spectral characteristics of white and blue LEDs used for the liquid-crystal display apparatuses and the like exhibit a peak wavelength of approximately 450 nm (the wavelength with the highest spectral radiance). That is, the peak wavelength in the spectral characteristics of white and blue LEDs is close to the peak wavelength in the hazard function (the wavelength with the highest degree of adverse effect of light on human bodies). Thus, light emitted from white or blue LEDs is considered to notably seriously affect the human bodies.
Japanese Patent Application Laid-open No. 2002-366129 discloses a technique for issuing a warning in a case where a cumulative time for VDT (visual display terminals such as personal computers) operations reaches a threshold. However, the technique disclosed in Japanese Patent Application Laid-open No. 2002-366129 takes into account only the cumulative time for the VDT operations and not colors contained in a display target image. Thus, in a case where a user of an image display apparatus continuously views displayed images (images displayed on a screen) containing much blue color for a long time, the warning may fail to be issued because the cumulative time for VDT operations has not reached the threshold. As a result, health hazards caused by light of a predetermined color such as blue light fail to be effectively prevented.